Changes in the local structure and Li + ion dynamics in lithium manganese oxides prepared by mechanical milling

Abstract

XRD, 7Li MAS NMR, and electrical resistivity measurements were carried out to probe the local structure and the Li + ionic diffusion in lithium manganese oxide Li 2MnO 3 prepared by mechanical milling and solid state reaction. XRD profiles and NMR spectra remarkably changed as milling time increased, and it is suggested that a disordered frame structure consisting of Mn–O polyhedral blocks was produced. Such a precursor would enable one to synthesize Li–Mn–O compounds at relatively lower temperatures compared to the synthesis just by solid state reaction. The activation energy for the hopping of the Li + ions in Li 2MnO 3 sintered at 900 °C was determined to be 0.46 eV from the analysis based on a simple Debye model of electrical resistivity. Changes in the NMR spectra and the electrical resistivities suggest that the Li + ions begin to occupy available sites in the Mn–O block layer at low temperatures and located in those, forming the lithium layer sandwiched by oxygen layers, at high temperatures in Li 2MnO 3 prepared via mechanical milling. The establishment of the lithium layers plays an important role in a valid Li + ionic conduction in layered Li 2MnO 3.